In recent years, contents such as a movie and music recorded on a DVD or the like have become widely used, and therefore a reproducing apparatus capable of providing an ideal sense of localization and an ideal sense of a sound field while reproducing multi-channel audio in a living room or in a vehicle has been proposed. However, reproducing characteristics of such an apparatus are designed for one user and accordingly an ideal acoustical effect is not exerted on other users excluded from consideration. Thus, an apparatus to solve such a problem is proposed in patent document 1. Hereinafter, a sound reproducing apparatus disclosed in patent document 1 will be described with reference to drawings.
FIG. 9 shows a sound reproducing apparatus 1, which is disclosed in patent document 1, provided in a front seat of a vehicle. To be more specific, by making two passengers L1 and L2 in the vehicle as listeners hear signal B1, which is reproduced by a recording device, by their respective left ears and hear signal B2, which is reproduced by the recording device, by their respective right ears, a similar acoustical effect of contents stored in a recording device 2 is exerted on each of the passengers. In front of passengers L1 and L2, four speakers 3a, 3b, 3c, and 3d are provided and are connected to amplifiers 4a, 4b, 4c, and 4d, respectively. Each speaker is paired with a corresponding amplifier so as to form acoustic generation means. Meanwhile, acoustic information recorded by using a well-known binaural recording system is stored in the recording device 2. The recording device 2 is connected to each of the amplifiers 4a, 4b, 4c, and 4d via an inverse filter network 5 structured in a procedure described below.
When the inverse filter network is structured, an acoustic transfer function hij (i=1 to 4: a symbol representing an ear, j=1 to 4: a symbol representing a speaker) between each of the speakers 3a, 3b, 3c, and 3d and both ears of the passengers is calculated in advance. Here, only h11 to h41 are shown. With reference to FIG. 10, a method for calculating the acoustic transfer function hij is described. A test signal generator 6 connected to each of the amplifiers 4a, 4b, 4c, and 4d generates a wideband signal such as a white noise and calculates the acoustic transfer function hij by using sounds S1, S2, S3, and S4 generated from the speakers 3a, 3b, 3c, and 3d, respectively; and sounds M1, M2, M3, and M4 measured by both ears of dummy heads D1 and D2 which are placed in assumed positions of passengers. In practice, the amplifiers are each activated sequentially. In other words, when speaker 3a, for example, is activated, the other speakers 3b, 3c, and 3d are not activated. The generated sounds S1 to S4, the measured sounds M1 to M4, and the acoustic transfer function hij satisfy a relation represented by the following equation.
                              [                                                                      M                  1                                                                                                      M                  2                                                                                                      M                  3                                                                                                      M                  4                                                              ]                =                              [                                                                                h                    11                                                                                        h                    12                                                                                        h                    13                                                                                        h                    14                                                                                                                    h                    21                                                                                        h                    22                                                                                        h                    23                                                                                        h                    24                                                                                                                    h                    31                                                                                        h                    32                                                                                        h                    33                                                                                        h                    34                                                                                                                    h                    41                                                                                        h                    42                                                                                        h                    43                                                                                        h                    44                                                                        ]                    ⁡                      [                                                                                S                    1                                                                                                                    S                    2                                                                                                                    S                    3                                                                                                                    S                    4                                                                        ]                                              [                  equation          ⁢                                          ⁢          1                ]            
An effect to be exerted by the sound reproducing apparatus 1 shown in FIG. 9 is represented as follows.
                              [                                                                      M                  1                                                                                                      M                  2                                                                                                      M                  3                                                                                                      M                  4                                                              ]                =                              [                                                            1                                                  0                                                  0                                                  0                                                                              0                                                  1                                                  0                                                  0                                                                              0                                                  0                                                  1                                                  0                                                                              0                                                  0                                                  0                                                  1                                                      ]                    ⁡                      [                                                                                B                    1                                                                                                                    B                    2                                                                                                                    B                    1                                                                                                                    B                    2                                                                        ]                                              [                  equation          ⁢                                          ⁢          2                ]            Equation 2 is transformed as follows.
                              [                                                                      M                  1                                                                                                      M                  2                                                                                                      M                  3                                                                                                      M                  4                                                              ]                =                                                            [                                                                                                    h                        11                                                                                                            h                        12                                                                                                            h                        13                                                                                                            h                        14                                                                                                                                                h                        21                                                                                                            h                        22                                                                                                            h                        23                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        32                                                                                                            h                        33                                                                                                            h                        34                                                                                                                                                h                        41                                                                                                            h                        42                                                                                                            h                        43                                                                                                            h                        44                                                                                            ]                            ⁡                              [                                                                                                    h                        11                                                                                                            h                        12                                                                                                            h                        13                                                                                                            h                        14                                                                                                                                                h                        21                                                                                                            h                        22                                                                                                            h                        23                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        32                                                                                                            h                        33                                                                                                            h                        34                                                                                                                                                h                        41                                                                                                            h                        42                                                                                                            h                        43                                                                                                            h                        44                                                                                            ]                                                    -              1                                ⁡                      [                                                                                B                    1                                                                                                                    B                    2                                                                                                                    B                    1                                                                                                                    B                    2                                                                        ]                                              [                  equation          ⁢                                          ⁢          3                ]            Equation 1 is assigned to equation 3 as follows.
                              [                                                                      S                  1                                                                                                      S                  2                                                                                                      S                  3                                                                                                      S                  4                                                              ]                =                                            [                                                                                          h                      11                                                                                                  h                      12                                                                                                  h                      13                                                                                                  h                      14                                                                                                                                  h                      21                                                                                                  h                      22                                                                                                  h                      23                                                                                                  h                      24                                                                                                                                  h                      31                                                                                                  h                      32                                                                                                  h                      33                                                                                                  h                      34                                                                                                                                  h                      41                                                                                                  h                      42                                                                                                  h                      43                                                                                                  h                      44                                                                                  ]                                      -              1                                ⁡                      [                                                                                B                    1                                                                                                                    B                    2                                                                                                                    B                    1                                                                                                                    B                    2                                                                        ]                                              [                  equation          ⁢                                          ⁢          4                ]                                                      [                                                                                h                    11                                                                                        h                    12                                                                                        h                    13                                                                                        h                    14                                                                                                                    h                    21                                                                                        h                    22                                                                                        h                    23                                                                                        h                    24                                                                                                                    h                    31                                                                                        h                    32                                                                                        h                    33                                                                                        h                    34                                                                                                                    h                    41                                                                                        h                    42                                                                                        h                    43                                                                                        h                    44                                                                        ]                                -            1                          =                              1                                        H                                              ⁡                      [                                                                                H                    11                                                                                        H                    21                                                                                        H                    31                                                                                        H                    41                                                                                                                    H                    12                                                                                        H                    22                                                                                        H                    32                                                                                        H                    42                                                                                                                    H                    13                                                                                        H                    23                                                                                        H                    33                                                                                        H                    43                                                                                                                    H                    14                                                                                        H                    24                                                                                        H                    34                                                                                        H                    44                                                                        ]                                              [                  equation          ⁢                                          ⁢          5                ]            
Accordingly, when the inverse filter network 5 as shown in FIG. 9 is designed so as to satisfy equation 4 and is provided before the amplifiers 4a, 4b, 4c, and 4d, and a signal for a left ear and a signal for a right ear are inputted to the inverse filter network, as a substitute for an output from the test signal generator 6, the signal for the left ear and the signal for the right ear become a signal for a left ear and a signal for a right ear of each dummy head D1 and D2. The signal for the left ear and the signal for the right ear are inputted to a left-hand input section and a right-hand input section, respectively, of the inverse filter network 5 shown in FIG. 9. Elements which configure the inverse filter network 5 are each represented by the following equations.
                                        H                          =                                            h              11                        ⁢                                                                                                                    h                      22                                                                                                  h                      23                                                                                                  h                      24                                                                                                                                  h                      32                                                                                                  h                      33                                                                                                  h                      34                                                                                                                                  h                      42                                                                                                  h                      43                                                                                                  h                      44                                                                                                                  -                                    h              12                        ⁢                                                                                                                    h                      21                                                                                                  h                      23                                                                                                  h                      24                                                                                                                                  h                      31                                                                                                  h                      33                                                                                                  h                      34                                                                                                                                  h                      41                                                                                                  h                      43                                                                                                  h                      44                                                                                                                  +                                    h              13                        ⁢                                                                                                                    h                      21                                                                                                  h                      22                                                                                                  h                      24                                                                                                                                  h                      31                                                                                                  h                      32                                                                                                  h                      34                                                                                                                                  h                      41                                                                                                  h                      42                                                                                                  h                      44                                                                                                                  -                                    h              14                        ⁢                                                                                                                    h                      21                                                                                                  h                      22                                                                                                  h                      23                                                                                                                                  h                      31                                                                                                  h                      32                                                                                                  h                      33                                                                                                                                  h                      41                                                                                                  h                      42                                                                                                  h                      43                                                                                                                                            [                  equation          ⁢                                          ⁢          6                ]                                          H          11                =                  +                      {                                                            h                  22                                ⁢                                                                                                                                                h                          33                                                                                                                      h                          34                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                                                                  -                                                h                  23                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  +                                                h                  24                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          7                ]                                          H          12                =                  -                      {                                                            h                  21                                ⁢                                                                                                                                                h                          33                                                                                                                      h                          34                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                                                                  -                                                h                  23                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                                                                  +                                                h                  24                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          8                ]                                          H          13                =                  +                      {                                                            h                  21                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  -                                                h                  22                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                                                                  +                                                h                  24                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          9                ]                                          H          14                =                  -                      {                                                            h                  21                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                  -                                                h                  22                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          33                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                                                                  +                                                h                  23                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          10                ]                                          H          21                =                  -                      {                                                            h                  12                                ⁢                                                                                                                                                h                          33                                                                                                                      h                          34                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                                                                  -                                                h                  13                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          11                ]                                          H          22                =                  +                      {                                                            h                  11                                ⁢                                                                                                                                                h                          33                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  -                                                h                  13                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          33                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          12                ]                                          H          23                =                  -                      {                                                            h                  11                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  -                                                h                  12                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          13                ]                                          H          24                =                  +                      {                                                            h                  11                                ⁢                                                                                                                                                h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                  -                                                h                  12                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          33                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                                                                  +                                                h                  13                                ⁢                                                                                                                                                h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          14                ]                                          H          31                =                  +                      {                                                            h                  12                                ⁢                                                                                                                                                h                          23                                                                                                                      h                          24                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                                                                  -                                                h                  13                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          24                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          23                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          15                ]                                          H          32                =                  -                      {                                                            h                  11                                ⁢                                                                                                                                                h                          23                                                                                                                      h                          24                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                                                                  -                                                h                  13                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          24                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          23                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          16                ]                                          H          33                =                  +                      {                                                            h                  11                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          24                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                                                                  -                                                h                  12                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          24                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          22                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          17                ]                                          H          34                =                  -                      {                                                            h                  11                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          23                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                                                                  -                                                h                  12                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          23                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                                                                  +                                                h                  13                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          22                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          18                ]                                          H          41                =                  -                      {                                                            h                  12                                ⁢                                                                                                                                                h                          23                                                                                                                      h                          24                                                                                                                                                              h                          33                                                                                                                      h                          34                                                                                                                                                  -                                                h                  13                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          24                                                                                                                                                              h                          32                                                                                                                      h                          34                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          23                                                                                                                                                              h                          32                                                                                                                      h                          33                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          19                ]                                          H          42                =                  +                      {                                                            h                  11                                ⁢                                                                                                                                                h                          23                                                                                                                      h                          24                                                                                                                                                              h                          33                                                                                                                      h                          34                                                                                                                                                  -                                                h                  13                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          24                                                                                                                                                              h                          31                                                                                                                      h                          34                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          23                                                                                                                                                              h                          31                                                                                                                      h                          33                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          20                ]                                          H          43                =                  -                      {                                                            h                  11                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          24                                                                                                                                                              h                          32                                                                                                                      h                          34                                                                                                                                                  -                                                h                  12                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          24                                                                                                                                                              h                          31                                                                                                                      h                          34                                                                                                                                                  +                                                h                  14                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          22                                                                                                                                                              h                          41                                                                                                                      h                          32                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          21                ]                                          H          44                =                  +                      {                                                            h                  11                                ⁢                                                                                                                                                h                          22                                                                                                                      h                          23                                                                                                                                                              h                          32                                                                                                                      h                          33                                                                                                                                                  -                                                h                  12                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          23                                                                                                                                                              h                          31                                                                                                                      h                          33                                                                                                                                                  +                                                h                  13                                ⁢                                                                                                                                                h                          21                                                                                                                      h                          22                                                                                                                                                              h                          31                                                                                                                      h                          32                                                                                                                                                            }                                              [                  equation          ⁢                                          ⁢          22                ]            
When signal B1 and signal B2, both of which are binaural-recorded, are processed by the inverse filter network 5 having the configuration as described above, sounds at both ears of passenger L1 are B1 and B2, and sounds at both ears of passenger L2 are B1 and B2. Therefore, the original sound field where recording has been performed is experienced by passengers L1 and L2.
If the configuration disclosed in patent document 1 includes controlling means for processing an output from the recording device 2 so as to input the output to the inverse filter network 5 by using digital filters or the like simulating predetermined acoustic transfer functions, it becomes possible to position a sound image in a predetermined direction. FIG. 11 is a diagram showing an acoustic transfer function G1 between a virtual sound source 7 and the dummy head D1, and an acoustic transfer function G2 between a virtual sound source 7 and the dummy head D1. FIG. 12 is a diagram showing a sound reproducing apparatus for positioning a sound image in a predetermined direction. Identical components to those in FIG. 9 bear the identical reference characters. The predetermined acoustic transfer functions Gland G2 are set as coefficients in filters 8a and 8b, respectively. A monophonic sound source 9, in which not a binaural-recorded sound but a monophonic signal B0 is recorded, is used as a sound source. In the configuration shown in FIG. 12, a sound at a left ear position of each of passengers L1 and L2 is G1•B0 and a sound at a right ear position of each of passengers L1 and L2 is G2•B0. Therefore, each sound is listened as if the sound is coming from the direction of the virtual sound source shown in FIG. 7. As a matter of course, the monophonic signal B0 may be processed in advance by using the acoustic transfer functions G1 and G2, or the acoustic transfer functions G1 and G2 may be incorporated into the elements configuring the inverse filter network, in order to produce the same effect.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 6-165298